This application claims a priority to the provisional U.S. Patent Applications No. 61/152,518, filed Feb. 13, 2009, which is incorporated herein by reference in its entirety.
The present invention relates generally to wind turbines. More particularly, the present invention relates to the pitch angle adjustment systems and methods. These systems and methods adjust the turbine blade pitch angle with respect to the incoming wind in order to adjust the power produced by the turbine, thereby extending the useful operating range of the wind turbine.
Due to the concerns over global warming and the limited amount of fossil fuels, alternative methods of energy production are desired. One such alternative source of energy is the wind energy produced by wind turbines, which convert kinetic energy of the wind into electricity. The performance of a wind turbine is determined by many factors: size of the turbine blades, wind speed, type of the turbine (upwind or downwind), electrical generator's converting efficiency, and the orientation of the turbine blade relative to the incident angle of the wind—i.e. the pitch angle to the turbine blades. Power that can be extracted from the wind generally scales with wind speed. It can be shown that the total available power in wind stream is proportional to the third power of wind speed. Therefore, at very low wind speeds the available power is too small to economically run the turbine. At the other side of the wind speed range, at very high wind speeds, the available wind power exceeds the electrical generator rating, thus making it necessary to stop the turbine rotation. However, the useful operating range and operating efficiency of wind turbine can be extended by changing pitch angle of turbine blades, because overall efficiency of the wind turbine is also a function of the turbine blade pitch angle.
A variety of techniques for adjusting the pitch angle of turbine blades exist in the field. Some systems for changing the pitch angle of wind turbines use a hydraulically controlled rod which is connected to turbine blades in order to adjust pitch angle of the turbine blades. However, these mechanisms are located peripherally with respect to the turbine shaft, thus needing additional space. Furthermore, these systems do not operate in power down situation. Therefore, these systems are not capable of protecting the turbine if power is lost.
Some other systems have a mechanism for adjusting the pitch of all turbine blades simultaneously, but lack any feedback loop, hydraulic actuation, or ability to protect the turbine when power is lost. Some systems rely on a per-turbine-blade pairs of gears, consequently reducing the overall reliability of wind turbine by creating multiple potential failure points. Some other systems rely on the centrifugal forces of the turbine blades themselves to adjust the turbine blade pitch angle, but, having no feathering ability or a feedback loop, are vulnerable to runaway failure when wind speed increases above the electrical generator's rating.
Therefore, a need remains for systems that can adjust the pitch angle of the turbine blades, thus controlling the electrical generator's output, while being able to provide safe feathering at high wind speeds.